The Organic Light Emitting Display (OLED) possesses many outstanding properties of self-illumination, low driving voltage, high luminescence efficiency, short response time, high clarity and contrast, near 180° view angle, wide range of working temperature, applicability of flexible display and large scale full color display. The OLED is considered as the most potential display device.
The OLED can be categorized into two major types according to the driving methods, which are the Passive Matrix OLED (PMOLED) and the Active Matrix OLED (AMOLED), i.e. two types of the direct addressing and the Thin Film Transistor (TFT) matrix addressing. The AMOLED comprises pixels arranged in array and belongs to active display type, which has high lighting efficiency and is generally utilized for the large scale display devices of high resolution.
The AMOLED is a current driving element. When the electrical current flows through the organic light emitting diode, the organic light emitting diode emits light, and the brightness is determined according to the current flowing through the organic light emitting diode itself. Most of the present Integrated Circuits (IC) only transmit voltage signals. Therefore, the AMOLED pixel driving circuit needs to accomplish the task of converting the voltage signals into the current signals. The traditional AMOLED pixel driving circuit generally is 2T1C, which is a structure comprising two thin film transistors and one capacitor to convert the voltage into the current.
As shown in FIG. 1, which is a 2T1C pixel driving circuit employed for AMOLED, comprising a first thin film transistor T10, a second thin film transistor T20, a first capacitor C10 and an organic light emitting diode D10. The first thin film transistor T10 is a switch thin film transistor, and the second thin film transistor T20 is a drive thin film transistor, and the capacitor C10 is a storage capacitor. Specifically, a gate of the first thin film transistor T10 is electrically coupled to the scan signal Scan, and a source is electrically coupled to the data signal Data, and a source electrically coupled to the first node A; a gate of the second thin film transistor T20 is electrically coupled to the first node A, and a source is electrically coupled to power source voltage Ovdd, and a drain is electrically coupled to the second node B; an anode of the organic light emitting diode D10 is electrically coupled to the second node B, and a cathode is grounded; one end of the first capacitor C10 is electrically coupled to the first node, and the other end is electrically coupled to the second node B. Besides, a parasitic capacitance C20 is further formed at the two ends of the organic light emitting diode D10, and the parasitic capacitance C20 is coupled with the two ends of the organic light emitting diode D10 in parallel. As the AMOLED displays, the scan signal Scan controls the first thin film transistor T10 to be activated, and the data signal Data enters the gate of the second thin film transistor T20 and the first capacitor C10 via the first thin film transistor T10. Then, the first thin film transistor T10 is deactivated. With the storage function of the first capacitor C10, the gate voltage of the second thin film transistor T20 can remain to hold the data signal voltage to make the second thin film transistor T20 to be in the conducted state to drive the current to enter the organic light emitting diode D10 via the second thin film transistor T20 and to drive the organic light emitting diode D10 to emit light.
In the aforesaid OLED pixel driving method, the organic light emitting diode D10 is constantly in the aging state, and the aging levels of all the pixels are not consistent, and result in the phenomenon of image sticking to shorten the lifetime of the organic light emitting diode and to influence the display quality of the OLED display device.